1. Field of the Invention
The present invention is directed to a medical apparatus, such as a heart pacemaker, for stimulating a physiological event in a patient, and in particular to such an apparatus wherein the stimulation intensity is automatically adapted to the physical activity of the patient. A method for adapting the stimulation intensity to the physical activity is also disclosed.
2. Description of the Prior Art
A heart pacemaker is known from European Application 0 232 681 wherein the frequency at which a stimulation pulses are supplied to the heart of the pacemaker user is adjustable on the basis of the physical activity of the pacemaker user. The adaptation of the stimulation frequency at the beginning of physical activity is made on the basis of the difference between the temperature present in the interior of the patient and the temperature present in the region of the body periphery of the patient. For extended physical activity, the adaptation of the stimulation frequency is undertaken in a different manner, for example, with reference only to the temperature present in the interior of the patient.
A difference between the temperature in the interior of the body (i.e., in the body core) and the temperature in the region of the body periphery, with certain known exceptions, is always present. Changes in this temperature difference, however, need not necessarily be related to a change in the physical activity of the patient. There is the risk in the case in the aforementioned known heart pacemaker that the stimulation frequency will be altered without a corresponding change in the physical activity level being present. This need not necessarily represent a risk for the patient in whom the heart pacemaker is implanted, but will at least produce discomfort. A change in the temperature present in the interior of the body, such as the blood temperature, which is used in this know heart pacemaker for adapting the stimulation frequency to extended physical activity, also need not necessarily be based on a modified physical activity of the patient, so that the risk of mismatching the stimulation frequency to the current physical activity is present.